The present invention relates to a character display apparatus for a word processor system or the like.
Various types of word processor systems are known in the art. One such system is an automatic typewriter which comprises an electric typewriter combined with a memory unit. The typewriter functions such as backspace, reverse line feed and the like are used to correct typewritten mistakes by means of typeover. The edited script is stored in the memory and played back to produce a perfect typewritten page. Such a system suffers from various drawbacks in that the legibility of the page being initially typed and edited is quite poor due to multiple typeovers. As another drawback, the system is slow since the typewwriter is not available for input during playback.
To overcome these drawbacks, word processor systems comprising cathode ray tube (CRT) display screens have come into widespread use. The cathode ray tube displays one or more lines of characters and allows editing on the screen. Since typeover on a CRT display causes automatic erasure of the previous data, the line or page of character data being input and edited on the screen and exactly resembles the final printed page. After editing on the CRT screen, the page of characters is transferred to a memory and played back therefrom for printing on an electric typewriter or line printer.
A drawback has heretofore existed in the improved word processing systems comprising CRT display screens regarding character line format. Since various business, scientific and legal applications require different numbers of characters in each printed line, it has been standard procedure to either design specialized word processing systems for the various applications or to provide a universal word processing system which accomodates the maximum number of characters per line which may be required in any reasonable application. The number of characters per line may be as high as 150.
Compressing 150 characters into a line on a CRT screen, even using high resolution display circuitry, provides characters of very low visibility, especially when alphabetic characters are displayed in both upper and lower case. It may be impossible to distinguish a lower case "a" from a lower case "s," for example, due to the small display size and limited resolution. These two characters are adjacent on a standard typewriter keyboard, and a frequent typing error is to strike the "a" key rather than the "s" key and vice-versa. In a low visibility display such an error may go undetected during editing and the page printed incorrectly. If the printed page is not proofread, the undetected error may cause a serious problem in an important application. If the page is proofread and the error detected, the error must be corrected on the CRT screen and the entire page played back again to produce a correct printed copy. Such multiple editing is very inefficient from the standpoints of time and cost.
On the other hand, word processing systems are still so expensive that they are often leased rather than sold. Where a business or governmental concern acquires, for an example, a 96 character per line system which features improved visibility and is adequate for most applications, considerable disruption of operations may occur when an occasion arises in which it is necessary to produce a number of documents in 128 character per line format.